1. Field of the Invention
The present invention relates to an evaporative emission control device for an internal combustion engine, and more specifically, to a control for detecting leakage in an evaporative emission control device.
2. Description of the Related Art
In order to prevent the fuel evaporative gas evaporated in a fuel tank from being emitted into atmosphere, there has been provided an evaporative emission control device for an internal combustion engine, including a canister interposed in a purge passage connecting the fuel tank and an intake passage of an internal combustion engine; a canister shutoff valve that opens or closes the canister to lead or seal the inside of the canister into or against atmosphere; a fuel tank shutoff valve that connects or disconnects the fuel tank and the canister; and a purge control valve that opens or blocks the purge passage. During fueling, the evaporative emission control device opens the canister shutoff valve and the fuel tank shutoff valve and closes the purge control valve so that fuel evaporative gas runs towards the canister, and makes the canister absorb the fuel evaporative gas. During the operation of the internal combustion engine, the evaporative emission control device opens the canister shutoff valve and the purge control valve, and thus discharges the fuel evaporative gas absorbed by the canister into the intake passage of the internal combustion engine. This is how the device treats the fuel evaporative gas. Furthermore, the evaporative emission control device carries out leakage detection to prevent the gas from leaking outside the device.
When leakage is detected in a conventional vehicle that is moved only with the driving force of an internal combustion engine, the opening and closing of the canister shutoff valve, the fuel tank shutoff valve and the purge control valve are controlled during the operation of the internal combustion engine, and the inside of the purge passage and the fuel tank are brought under negative pressure by using the negative pressure created in the intake passage of the internal combustion engine. The leakage judgment is made on the basis of whether or not the negative pressure is maintained. In this manner, leakage is detected.
However, in a vehicle such as a plug-in hybrid vehicle that is equipped with a motor apart from the internal combustion engine and moved by using the driving force of the motor, the internal combustion engine is hardly operated to improve fuel consumption. For this reason, if the leakage detection of the evaporative emission control device is intended to be carried out during the operation of the internal combustion engine, there is less chance of the leakage detection, and this is not preferable.
To solve the foregoing issue, a technology has been developed, which provides a negative-pressure pump that depressurizes the inside of the evaporative emission control device, and detects leakage in the evaporative emission control device by controlling the actuation of the negative-pressure pump and the opening/closing of a canister shutoff valve, a fuel tank shutoff valve and a purge control valve when an ignition key is off (Japanese Patent No. 4107053).
In an evaporative fuel processor described in the above-mentioned publication, the negative-pressure pump is first actuated, and thus, leakage in a part (canister, for example) of the evaporative fuel processor is detected. Secondly, the entire evaporative fuel processor including the fuel tank is brought under negative pressure, thereby detecting leakage in the entire evaporative fuel processor including the fuel tank.
However, if the leakage detection is applied to the entire evaporative fuel processor including the fuel tank after the leakage detection in a part of the evaporative fuel processor is finished, it takes time to carry out the leakage detection. Considering that the negative-pressure pump is actuated during leakage detection, the prolongation of leakage detection is undesirable as it leads to the power consumption of the batteries installed in a vehicle.